Various types of biometric systems are used more and more in order to provide for increased security and/or enhanced user convenience.
In particular, fingerprint sensing systems have been adopted in, for example, consumer electronic devices, thanks to their small form factor, high performance, and user acceptance.
To save cost and valuable surface space, there is an effort towards smaller and smaller fingerprint sensors, which may be substantially smaller than the user's fingerprint.
One way of achieving satisfactory biometric performance with a small fingerprint sensor is to provide a so-called swipe sensor or strip sensor. By instructing the user to swipe his finger across the sensor surface and capturing image slices during the swiping motion sufficient fingerprint information can be collected.
For some applications, however, swiping the finger across the sensor may not be considered to be sufficiently intuitive and simple to the user.
For such and other applications, fingerprint sensing systems employing small sensors for stationary finger placement have been proposed. In such fingerprint sensing systems, the user may be authenticated against an enrolled fingerprint representation (often referred to as a template) based on a single partial fingerprint image from the sensor.
For achieving the desired satisfactory biometric performance when authenticating based on a single partial fingerprint image from a small fingerprint sensor, it may be necessary that the enrolled template corresponds to a considerably larger portion of the user's fingerprint than the partial fingerprint image captured in connection with an authentication attempt.
One way of achieving such a larger enrolled template is to enroll users on a larger fingerprint sensor. This approach is, however, not suitable for many applications where enrollment and authentication should be carried out using the same electronic device, such as a mobile communication device.
It has therefore been proposed to combine several partial images from corresponding finger placements on a small fingerprint sensor to form a combined template for enrollment. It has, however, been found that it may sometimes be difficult to combine the partial images for various reasons.
US 2014/0003678 discloses an enrollment method in which navigation information from one or more navigation sensors is used to determine if there has been finger motion, including rotation, between partial fingerprint images. If there has been motion between images, the partial fingerprint image is adjusted using the navigation information.
However, there appears to still be room for improvement. In particular, it would be desirable to provide for a facilitated combination of partial fingerprint images, resulting in an enrollment procedure that is more convenient for the user.